Mixing device promoting a homogeneous distribution of a diphasic mixture, heat exchange facility and associated mixing method

ABSTRACT

A mixing device for distributing a mixture of a first phase and a second phase of a first fluid in a longitudinal direction in at least one passage of a heat exchanger, said mixing device including at least one lateral channel configured for the first phase to flow from at least one first inlet; a series of longitudinal channels extending in the longitudinal direction and each configured for the second phase to flow from a second inlet to a second outlet, said longitudinal channels succeeding each other in a lateral direction orthogonal to the longitudinal direction; and at least one opening fluidly connecting said lateral channel to at least one longitudinal channel such that the mixing device is configured to distribute a mixture of the first phase and the second phase via the second outlet of said longitudinal channel.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 371 of International Application No. PCT/EP2020/084935, filed Dec. 7, 2020, which claims priority to French Patent Application No. 1914897, filed Dec. 19, 2019, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present invention relates to a mixing device for more homogeneously distributing a mixture of two liquid/gaseous phases in at least one passage of a heat exchanger and to a heat exchange facility comprising such a mixing device.

In particular, the present invention can be applied to a heat exchanger that vaporizes at least one flow of a liquid-gas mixture, in particular a flow of a liquid-gas mixture with a plurality of constituent elements, for example, a mixture comprising hydrocarbons, by exchanging heat with at least one other fluid, for example, natural gas, that cools, or even at least partly liquefies, or even liquefied natural gas that sub-cools.

Among the methods using one or more fluid refrigeration cycle(s) with diphasic coolant, i.e. in the liquid/gas mixture state, several methods for liquefying a natural gas stream in order to obtain liquefied natural gas (LNG) are known. Typically, a cooling stream, generally a mixture with a plurality of constituent elements, such as a mixture containing hydrocarbons, is compressed by a compressor and then introduced into an exchanger or a series of exchangers where it is completely liquefied and sub-cooled to the coldest temperature of the method that is reached by the fluids that cool, typically that of the liquefied natural gas stream. At the coldest outlet of the exchanger, the cooling stream is expanded by forming a first phase and a second phase. These two phases are separated by means of a phase separator and then reintroduced into the exchanger and remixed before being reintroduced into the exchanger. The cooling stream introduced into the exchanger in the diphasic state is vaporized therein against the hydrocarbon stream that liquefies and against the natural gas. Document WO-A-2017/081374 describes one of these known methods.

The use of brazed plate and fin aluminum exchangers allows very compact devices to be provided that provide a large exchange surface, thereby improving the energy performance capabilities of the method, and so doing in a limited volume.

These exchangers comprise a stack of plates that extend in two dimensions, length and width, thus forming a stack of a plurality of sets of passages positioned on top of each other, with some being intended for circulating a heat transfer fluid, for example, the hydrocarbon stream to be liquefied, and others being intended for circulating a coolant, for example, the diphasic cooling stream to be vaporized.

Heat exchange structures, such as heat exchange corrugations, are generally arranged in the passages of the exchanger. These structures comprise fins that extend between the plates of the exchanger and allow the heat exchange surface area of the exchanger to be increased. They also function as spacers and contribute to the mechanical strength of the passages.

Some issues arise in exchangers implementing cooling streams of a diphasic nature, in particular when their vaporization occurs in an ascending vertical flow.

Indeed, in order to ensure that the exchanger operates correctly, i.e. in particular to maximize the use of its exchange surface, in particular for an exchanger implementing a liquid-gas mixture, the proportion of liquid phase and gaseous phase must be the same in all the passages and must be uniform within the same passage.

The dimensioning of the exchanger is computed assuming a uniform distribution of the phases, and thus a single temperature at the end of vaporization of the liquid phase per passage, equal to the dew point of the mixture.

For a mixture with a plurality of constituent elements in particular, the end of vaporization temperature will depend on the proportion of liquid phase and gaseous phase in the passages, since the two phases do not have the same compositions.

In the event of uneven distribution of the two phases, the temperature profile of the first fluid will therefore vary depending on the passages and/or within the same passage. Due to this non-uniform distribution, the one or more fluid(s) in an exchange relationship with the two-phase mixture can have an exchanger outlet temperature that is higher than the expected temperature, which consequently degrades the performance capabilities of the heat exchanger.

One solution for distributing the liquid and gaseous phases of the mixture as evenly as possible involves separately introducing them into the exchanger and then mixing them together only once they are inside the exchanger.

Documents FR-A-2563620 or WO-A-2018/172644 describe such exchangers, in which a grooved bar is inserted into the series of passages for channeling the two-phase mixture. This mixing device comprises a series of separate channels or grooves for the flow of the liquid phase of the coolant and another series of separate channels for the flow of the gaseous phase of the coolant. The channels of one series are fluidly connected to channels of the other series via openings so that a liquid-gas mixture, i.e. a diphasic stream, is distributed out of the mixing device toward the heat exchange area. Each coolant passage of the exchanger is provided with such a device.

One problem that arises with this type of mixing device relates to the uneven distribution of the liquid-gas mixture in the width of the exchanger passages.

Indeed, the two-phase mixture is distributed at the outlet of the channels emerging into the passage. Since the channels are arranged at a certain distance from each other, the liquid-gas mixture is discretely introduced into the exchange zone over the width of the passage. As the fluid flows in the overall direction of flow in the exchanger, a distribution can occur in the direction orthogonal to the overall direction of flow, in particular by virtue of the exchange corrugations that are generally used in this type of exchanger, such as perforated or serrated corrugations. Thus, the “serrated” type corrugations tend to deflect a portion of the fluid from its direction of flow and the perforated corrugations fluidly connect the channels formed by the corrugations.

However, homogenization of the fluid distribution over the width of the exchanger is only achieved after the mixture travels a certain distance after exiting the mixing device. Over this distance, the fluid supplies the exchange zone with uneven mass flow rates depending on the considered position in the width of the exchanger, some channels of the exchange corrugations may have a limited or even no supply. The performance capabilities of the exchanger are degraded. Furthermore, such distribution by lateral deflection of the fluid is not possible with straight unperforated corrugations.

Exchangers working subject to low temperature deviations between the heat transfer and coolant fluids are even more sensitive to this poor distribution phenomenon. In addition, the phenomenon of inhomogeneous distribution is accentuated in the case of a coolant mixture with a plurality of constituent elements.

None of the existing solutions is satisfactory. Thus, arranging a free space at the outlet of the mixing device raises problems in terms of the mechanical strength of the exchanger and can lead to the first phase accumulating in this zone, Increasing the number of channels succeeding each other in the width of the exchanger leads to a reduction in the flow rate of the first phase through each opening of each channel and is detrimental to proper distribution of the diphasic mixture at the outlet of the mixing device. Finally, the “hardway” type of corrugation arrangement at the outlet of the mixing device or the arrangement of mixing devices with more complex geometry increases pressure losses, which degrades the performance capabilities of the method.

SUMMARY

The aim of the present invention is to address all or some of the aforementioned problems, in particular by proposing a mixing device providing more homogeneous distribution of a diphasic mixture in the width of a heat exchanger passage, while limiting the pressure losses that the diphasic mixture can experience at the outlet of the mixing device.

The solution according to the invention then involves a mixing device for distributing a mixture of a first phase and a second phase of a first fluid generally in a longitudinal direction in at least one passage of a heat exchanger, said mixing device comprising:

-   -   at least one lateral channel configured for a first phase of the         first fluid to flow from at least one first inlet;     -   a series of longitudinal channels extending in the longitudinal         direction and each configured for the second phase of the first         fluid to flow from a second inlet to a second outlet, said         longitudinal channels succeeding each other in a lateral         direction orthogonal to the longitudinal direction; and     -   at least one opening fluidly connecting said lateral channel to         at least one longitudinal channel such that the mixing device is         configured to distribute a mixture of the first phase and the         second phase via the second outlet of said at least one         longitudinal channel, characterized in that said at least one         longitudinal channel of the mixing device is divided, in the         longitudinal direction, into an upstream portion and a         downstream portion each having a length measured in the         longitudinal direction and a width measured in the lateral         direction, with the downstream portion being arranged between         the upstream portion and the second outlet, said downstream         portion having, at any point of its length, a width that is         greater than the width of the upstream portion.

As applicable, the invention can comprise one or more of the following features:

-   -   the downstream portion has an increasing width, preferably         continuously increasing, over its length toward the second         outlet;     -   the downstream portion has a minimum width and a maximum width,         with the ratio D_(M)/D_(m) being greater than or equal to 1.1,         preferably greater than or equal to 1.8 and/or less than or         equal to 4;     -   all or part of the downstream portion has, as a longitudinal         section in a plane parallel to the longitudinal direction and to         the lateral direction, an external profile in the form of an         isosceles trapezoid;     -   all or part of the downstream portion has, as a longitudinal         section in a plane parallel to the longitudinal direction and to         the lateral direction, a curvilinear external profile;     -   the downstream portion emerges at a downstream face of the         mixing device, the external profile forming an angle, measured         between the tangent to said external profile at the point of         intersection with the downstream face and the axis of symmetry         of the longitudinal channel, ranging between 5 and 85°;     -   the upstream portion of the longitudinal channel is connected to         the downstream portion by one end, said at least one opening         emerging into said longitudinal channel at the upstream portion         at a distance from the end, preferably the distance is greater         than or equal to 4% and preferably ranges between 7 and 90% of         the length of the upstream portion;     -   at least one opening is arranged such that, when the first phase         flows from the first inlet of the lateral channel and the second         phase flows from the second inlet of the longitudinal channel,         the mixing of the first phase and the second phase occurs         upstream of the downstream portion;     -   the one or more opening(s) of the mixing device all emerge at         the upstream portion of a longitudinal channel;     -   each longitudinal channel of the series of longitudinal channels         comprises at least one opening emerging at its upstream portion,         with the position of the at least one opening in the         longitudinal direction varying between the longitudinal         channels;     -   length of the upstream portion and the length of the downstream         portion are such that the ratio L₃/L₄ ranges between 1 and 15,         preferably between 3 and 12;     -   all or part of the upstream portion has, as a longitudinal         section in a plane parallel to the longitudinal direction and to         the lateral direction, a straight external profile with a         constant width that is preferably equal to the minimum width of         the downstream portion;     -   the downstream portion has a depth, measured in a direction,         called stacking direction, that is perpendicular to the         longitudinal direction and perpendicular to the lateral         direction, increasing toward the second outlet;     -   the longitudinal channel comprises at least one obstacle         arranged so as to sub-divide the downstream portion into a         plurality of intermediate channels emerging at the second         outlet, preferably said intermediate channels are arranged         symmetrically with respect to the axis of symmetry of the         longitudinal channel;     -   at the second outlet, the total surface of said at least one         obstacle measured in a transverse section plane perpendicular to         the longitudinal direction is between 20 and 80%, preferably         between 30 and 70%, of the total fluid passage section of the         surface of the downstream portion measured in said transverse         section plane;     -   the width of the at least one obstacle, measured in the lateral         direction, increases toward the second outlet, with at least one         obstacle preferably having, along a longitudinal section plane,         a curvilinear external profile;     -   the longitudinal channel further comprises at least one         balancing channel fluidly connecting the intermediate channels.

Furthermore, the invention relates to a heat exchanger comprising a plurality of plates arranged parallel to each other and to a longitudinal direction, said plates being stacked in a spaced-apart manner so as to together define at least one first set of passages configured for the first fluid to generally flow in the longitudinal direction and at least one second set of passages configured for the flow of a second fluid to be brought into a heat exchange relationship with the first fluid, with at least one passage of the first set comprising a mixing device according to the invention.

Moreover, the invention relates to a heat exchange facility comprising:

-   -   a heat exchanger comprising a plurality of plates arranged         parallel to each other and to a longitudinal direction, said         plates being stacked in a spaced-apart manner so as to together         define at least one first set of passages configured for a first         fluid to generally flow in the longitudinal direction and at         least one second set of passages configured for the flow of a         second fluid to be brought into a heat exchange relationship         with the first fluid;     -   a source of a first phase of the first fluid fluidly connected         to at least one first manifold of the heat exchanger;     -   a source of a second phase of the first fluid fluidly connected         to at least one second manifold of the heat exchanger;     -   a mixing device according to the invention, said mixing device         being arranged in at least one passage of the first series and         being configured to distribute the first fluid formed by a         mixture of the first phase and the second phase in said passage         of the first series, the first inlet of the lateral channel         being in fluid communication with said first manifold, and the         second inlet being in fluid communication with the second         manifold, the first phase being a liquid phase and the second         phase being a gaseous phase.

Preferably, the first phase is a liquid phase. The second phase is a gaseous phase.

According to another aspect, the invention relates to a method for mixing a first phase and a second phase of a first fluid in a mixing device according to the invention, said method comprising the following steps:

i) introducing the first phase of the first fluid via at least one first inlet of the lateral channel;

ii) introducing the second phase of the first fluid via a second inlet of each longitudinal channel, the second phase flowing in each longitudinal channel in the longitudinal direction to a second outlet of said longitudinal channel;

iii) flowing at least part of the first phase from the lateral channel toward the longitudinal channel via the opening so as to mix the first phase with the second phase in the longitudinal channel;

iv) distributing the mixture of the first phase and the second phase via the second outlet of each longitudinal channel.

Preferably, the first phase is mixed with the second phase upstream of the downstream portion.

Moreover, the invention also relates to a method for liquefying a hydrocarbon stream, such as natural gas, as a second fluid by exchanging heat with at least one diphasic cooling stream as a first fluid, said method implementing a mixing method according to the invention and comprising the following steps:

a) introducing the hydrocarbon stream into a second set of passages of a heat exchanger;

b) introducing a cooling stream into a third set of passages of the heat exchanger;

c) discharging the cooling stream from the heat exchanger and expanding the cooling stream to at least one pressure level so as to produce at least one diphasic cooling stream;

d) separating at least part of the diphasic cooling stream originating from step c) into a second phase and a first phase;

e) arranging a mixing device in at least one passage of a first set of passages of the heat exchanger;

f) introducing at least part of the second phase and at least part of the first phase into the mixing device so as to obtain a first fluid formed by a mixture of the first phase and the second phase at the outlet of the mixing device;

g) vaporizing at least part of the first fluid originating from step f) in the passage by exchanging heat with at least the hydrocarbon stream so as to obtain a cooled and/or at least partially liquefied hydrocarbon stream at the outlet of the exchanger.

The expression “natural gas” refers to any composition containing hydrocarbons, including methane at least. This comprises a “raw” composition (prior to any treatment or scrubbing) and also any composition that has been partially, substantially or totally treated for reducing and/or eliminating one or more compounds, including, but without being limited to, sulfur, carbon dioxide, water, mercury and certain heavy and aromatic hydrocarbons.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be better understood by virtue of the following description, which is given purely by way of a non-limiting example and with reference to the appended figures, in which:

FIG. 1 schematically shows a heat exchange facility according to one embodiment of the invention;

FIG. 2 is a three-dimensional schematic view of a mixing device according to one embodiment of the invention;

FIG. 3 is a schematic transverse section view, in a plane perpendicular to the plates of the exchanger, of a first mixing device according to one embodiment of the invention;

FIG. 4 is a schematic longitudinal section view in a plane parallel to the longitudinal direction z and the lateral direction y of a mixing device according to one embodiment of the invention;

FIG. 5 is a schematic longitudinal section view in a plane parallel to the longitudinal direction z and the lateral direction y of a mixing device according to another embodiment of the invention;

FIG. 6 is a schematic longitudinal section view in a plane parallel to the longitudinal direction z and the lateral direction y of a mixing device according to another embodiment of the invention;

FIG. 7 is a schematic longitudinal section view in a plane parallel to the longitudinal direction z and the lateral direction y of a mixing device according to another embodiment of the invention;

FIG. 8 is a schematic longitudinal section view in a plane parallel to the longitudinal direction z and the lateral direction y of a mixing device according to another embodiment of the invention;

FIG. 9 is a schematic longitudinal section view in a plane parallel to the longitudinal direction z and the lateral direction y of a mixing device according to another embodiment of the invention;

FIG. 10 shows a configuration of a mixing device and exchanger according to the invention used to perform fluid flow simulations;

FIG. 11 shows the results of fluid flow simulations with a mixing device configured according to the prior art and with a mixing device according to one embodiment of the invention;

FIG. 12 schematically shows a method for liquefying a hydrocarbon stream according to one embodiment of the invention;

FIG. 13 schematically shows a method for liquefying a hydrocarbon stream according to another embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a section view of a heat exchanger 1 comprising a mixing device 3 according to the invention. The exchanger 1 is preferably of the type with brazed plates and fins. It comprises a stack of plates 2 (not shown) that extend in two dimensions, parallel to a plane defined by a longitudinal direction z and a lateral direction y. The plates 2 are arranged parallel, one above the other, with a spacing between each plate and thus form a stack of passages for the flow of fluids in an indirect heat exchange relationship via said plates.

Preferably, each passage has a parallelepiped and flat shape. The gap between two successive plates is small compared to the length, measured in the longitudinal direction z, and the width, measured in the lateral direction y, of each passage.

The exchanger 1 can comprise more than 20 plates, or even more than 100, together defining a first set of passages 10 (a single passage is shown in FIG. 1 ) for channeling at least one first fluid F1, and a second set of passages 20 (not shown in FIG. 1 ) for channeling at least one second fluid F2, with the flow of said fluids generally occurring in the direction z. The passages 10 can be arranged, in whole or in part, alternately and/or adjacent to all or some of the passages 20. The exchanger 1 can comprise a third set of passages, or even more, for the flow of one or more additional fluid(s). These sets of passages are stacked relative to each other forming a stack of passages.

The seal for the passages 10, 20 along the edges of the plates 2 is generally provided by lateral and longitudinal sealing strips 4 attached to the plates 2. The lateral sealing strips 4 do not completely seal the passages 10, 20 but advantageously leave fluid inlet and outlet openings located in the diagonally opposite corners of the passages.

The openings of the passages 10 of the first set are arranged so as to coincide one above the other in the stacking direction x of the passages, which is perpendicular to the directions y and z, while the openings of the passages 20 of the second set are arranged in the other corners of the exchanger located in FIG. 1 by the arrows F2, with the inlet and the outlet for the second fluid F2 being respectively located on the top left-hand side and the bottom right-hand side. The openings placed one above the other are respectively joined in semi-tubular manifolds 40, 45, 52, 55, through which the fluids are distributed and discharged into and from the passages 10, 20.

It should be noted that configurations for introducing and discharging fluids other than that shown in FIG. 1 can be used. The openings of the passages thus can be arranged at other positions in the width of the exchanger, in particular at the center of the width of the exchanger, and/or at other positions in the length of the exchanger.

In the illustration of FIG. 1 , the semi-tubular manifolds 52 and 45 are used to introduce fluids into the exchanger 1 and the semi-tubular manifolds 40, 55 are used to discharge these fluids out of the exchanger 1.

In this alternative embodiment, the manifold supplying one of the fluids and the manifold discharging the other fluid are located at the same end of the exchanger, with the fluids F1, F2 thus flowing counter-currently through the exchanger 1.

According to another alternative embodiment, the first and second fluids can also circulate co-currently, with the means for supplying one of the fluids and the means for discharging the other fluid then being located at opposite ends of the exchanger 1.

Preferably, the direction z is oriented vertically when the exchanger 1 is operating. The first fluid F1 generally flows vertically and upwardly, Other flow directions and courses of the fluids F1, F2 obviously can be contemplated, without departing from the scope of the present invention.

It should be noted that, within the scope of the invention, one or more second fluid(s) F2 with different natures can flow within the passages 20 of the second set.

Preferably, the first fluid F1 is a coolant and the second fluid F2 is a heat transfer fluid.

The exchanger advantageously comprises distribution corrugations 51, 54, arranged between two successive plates 2 in the form of corrugated sheets, which extend from the inlet and outlet openings. The distribution corrugations 51, 54 ensure the uniform distribution and recovery of the fluids over the entire width of the passages 10, 20.

Furthermore, the passages 10, 20 advantageously comprise heat exchange structures arranged between the plates 2. The purpose of these structures is to increase the heat exchange surface of the exchanger and to increase the exchange coefficients between the fluids by making the flows more turbulent. Indeed, the heat exchange structures are in contact with the fluids circulating in the passages and transfer thermal flows by conduction up to the adjacent plates 2, to which they can be attached by brazing, which increases the mechanical strength of the exchanger.

The heat exchange structures also act as spacers between the plates 2, in particular when assembling the exchanger by brazing and to avoid any deformation of the plates when implementing pressurized fluids. They also provide guidance for the flows of fluid in the passages of the exchanger.

Preferably, these structures comprise heat exchange corrugations 11, which advantageously extend over the width and the length of the passages 10, 20, parallel to the plates 2, in the extension of the distribution corrugations over the length of the passages. The passages 10, 20 of the exchanger thus have a main part of their length forming the heat exchange part itself, which is lined with a heat exchange structure, with said main part being bordered by distribution parts lined with the distribution corrugations 51, 54.

FIG. 1 shows a passage 10 of the first set configured for the flow of a first fluid F1 in the form of a mixture of two phases, also called a diphasic mixture. The first set comprises a plurality of such passages 10 stacked one above the other. The first fluid F1 is separated, in a separator device 6, into a first phase 61 and a second phase 62 separately introduced into the exchanger 1 by means of a separate first manifold 30 and second manifold 52. The separator 6 then forms a first phase and a second phase source. The term “source” of fluid means any means adapted to supply the channels of the mixing device with a fluid.

Preferably, the first phase 61 is liquid and the second phase 62 is gaseous. In the case whereby the longitudinal channel is configured for a vertical and upward flow of the first phase and of the diphasic mixture at the second outlet, gravity has less impact on the flow of the gaseous phase relative to that of the liquid phase. The conveyance of the liquid phase in the opening 34 is facilitated by the greater speed of the gaseous phase. Furthermore, the presence of the gaseous phase facilitates the flow of the liquid phase once said liquid phase has been introduced into the longitudinal channel via the opening 34.

The phases 61, 62 are then mixed together by means of a mixing device 3 arranged in at least one passage 10. Advantageously, several passages 10, or even all the passages 10, of the first set comprise a mixing device 3. The semi-tubular manifolds 52 and 55 are fluidly connected to the inlets and outlets of the passages 10. The first manifold 30 is fluidly connected to at least one first inlet 311 of the mixing device 3. The second manifold 52 is fluidly connected to at least one second inlet 321 of the mixing device 3. The first and second manifolds can be any manifold means adapted to collect fluid from a fluid source and introduce said fluid into one or more passage(s) of a heat exchanger.

It should be noted that FIG. 1 shows a mixing device 3 positioned at a certain distance from the distribution zone 51 of the exchanger 1. According to an alternative embodiment, the mixing device 3 can be positioned directly after the distribution zone, or juxtaposed with said zone, that is by being a single piece with the distribution zone. According to this latter possibility, the mixing device forms a one-piece part, which can be manufactured by conventional machining or by additive manufacturing, i.e. by 3D printing, for example, by laser sintering.

FIG. 2 is a three-dimensional view of a mixing device 3 advantageously made up of a bar, or rod, housed in a passage 10.

The mixing device 3 preferably extends into the section of the passage 10 over almost all, or even all, the height of the passage 10, so that the mixing device is in contact with each plate 2 forming the passage 10.

The mixing device 3 is advantageously attached to the plates 2 by brazing.

The mixing device 3 advantageously has an overall parallelepiped shape.

Preferably, the mixing device 3 is a one-piece part, i.e. formed by a block or as a single piece. The mixing device 3 can be manufactured by conventional machining or by additive manufacturing. The mixing device 3 can have, parallel to the longitudinal direction z, a first dimension ranging between 20 and 200 mm and, parallel to the lateral direction y, a second dimension ranging between 100 and 1,400 mm. The mixing device 3 comprises at least one lateral channel 31 configured for the first phase 61 of the first fluid F1 to flow from at least one first inlet 311. Preferably, the lateral channel 31 extends parallel to the lateral direction y.

It further comprises a series of longitudinal channels 32 extending parallel to the longitudinal direction z and configured for the second phase 62 of the first fluid F1 to flow from a second inlet 321 up to a second outlet 322, with said longitudinal channels 32 being arranged at successive positions y_(i), y_(i+1), . . . in the lateral direction y.

Preferably, the lateral channel 31 extends over the entire second dimension and/or the longitudinal channel 32 extends over the entire first dimension.

Preferably, the mixing device 3 comprises at least one first inlet 311 in fluid communication with the first manifold 30 and a second inlet 321, separate, i.e. distinct, from the first inlet 311, in fluid communication with the second manifold 52. The first manifold 30 is fluidly connected to a first phase source 61 and the second manifold 52 is fluidly connected to another second phase source 62. Said at least one first inlet 311 and said at least one second inlet 321 are brought into fluid communication via at least one opening 34. In fact, the mixing device is configured for separate introduction of the first phase and the second phase, with the first inlet 311 being adapted for supplying the lateral channel 31 in the first phase 61 and said at least one second inlet 321 being adapted for supplying the longitudinal channels 32 in the second phase 62.

The first and second inlets are advantageously formed by causing the lateral and longitudinal channels to emerge at the lateral and longitudinal peripheral edges of the device 3.

FIG. 2 shows the introduction of the first phase 61 via an end of the device 3 comprising a plurality of first inlets 311. According to an advantageous embodiment, the mixing device 3 comprises at least one other first inlet for the first phase 61 located at an opposite end of the device 3. Advantageously, these other inlets are obtained by extending the lateral channels 31 until they emerge at an opposite lateral edge of the exchanger 1. In this case, another first manifold 30 is arranged on an opposite side of the exchanger 1. Introducing the first phase 61 on either side of the mixing device allows the effect of the pressure losses to be reduced when the first phase flows in the lateral channels, which promotes more homogeneous distribution of the diphasic mixture over the width of the exchanger.

Preferably, the mixing device 3 comprises a mixing volume located in the longitudinal channel 32, downstream of the opening 34 in the direction of flow of the first phase 61 in the opening 34.

The lateral channel 31 is fluidly connected to at least one longitudinal channel 32 such that, when the first phase 61 flows in the lateral channel 31 and the second phase 62 flows in the longitudinal channel 32, the mixing device 3 distributes, via a second outlet 322 of the channel 32, a mixture of the first phase 61 and the second phase 62, preferably a two-phase liquid/gas mixture F1, also called a diphasic mixture. Preferably, the longitudinal channel and/or the lateral channel are generally straight.

The channels 31, 32 are advantageously in the form of longitudinal recesses provided in the mixing device 3. They preferably emerge at the upper 3 a and lower 3 b surfaces of the mixing device 3.

Preferably, the channels 31, 32 have a square or rectangular transverse section, but optionally can assume other shapes (round, round portion, etc.).

The openings 34 advantageously are perforations 34 made in the material of the device 3 and extending between the first channel 31 and the second channel 32, preferably in the plane formed by the directions x and y, with the openings 34 being able to be inclined with respect to the direction x or, preferably, to be aligned with the vertical direction x. Preferably, the openings 34 have cylindrical symmetry, and more preferably are cylindrical.

Preferably, said at least one lateral channel 31 comprises a bottom wall 3 c and said at least one longitudinal channel 32 comprises a top wall 3 d, which extends opposite the bottom wall 3 c, with the openings 34 being perforated in the bottom wall of the first channel 31 and emerging into the top wall of the longitudinal channel 32.

FIG. 3 is a view of the mixing device 3 of FIG. 2 in a section plane orthogonal to the lateral direction y and passing through an opening 34.

According to the prior art, mixing devices 3 are arranged in the passages 10 of the first set, with said mixing devices having longitudinal channels, the width of which, measured in the lateral direction y, remains constant in the longitudinal direction z, in particular longitudinal channels of parallelepiped shape such as the shape of the lateral channels 31 shown in FIG. 2 .

At the outlet of each longitudinal channel 32, the flow of the two-phase mixture of the first fluid F1 preferably occurs in the longitudinal direction z, with a gradual expansion of the flow in the width of the passage 10. The homogenization of the flows in each passage is only obtained beyond a certain distance covered by the mixture. This lack of homogenization of the mixture F1 occurs throughout the stack of passages 10 of the first set.

In order to address these problems, the present invention proposes arranging a mixing device 3 in a passage 10 of the first set, with at least one longitudinal channel 32 of the mixing device being divided, in the longitudinal direction z, into an upstream portion 323 and a downstream portion 324, each having a length L₃, L₄ measured in the longitudinal direction z and a width D₃, D_(y) measured parallel to the lateral direction y, with the downstream portion 324 being arranged between the upstream portion 323 and the second outlet 322. According to the invention, the downstream portion 324 has, at any point of its length L₄, a width D_(y) that is (strictly) greater than the width D₃ of the upstream portion 323.

It should be noted that the term “width” is understood to mean the distance measured between the edges defining the longitudinal channel 32 in a predetermined longitudinal section plane that is parallel to the longitudinal direction z and parallel to the lateral direction y, i.e. the width of the external profile of the channel in said section plane, as shown in FIG. 4 to FIG. 9 , for example.

Arranging a downstream portion with a widening in the lateral direction promotes lateral expansion of the diphasic mixture exiting the longitudinal channel 32. The inventors of the present invention have demonstrated that the fluid jet formed a wider base cone at the outlet of the longitudinal channel, which allowed the fluid exiting the longitudinal channel 32 to irrigate a larger number of exchange channels of an exchange corrugation positioned, during operation, downstream of the mixing device 3. It is thus possible to obtain faster homogenization with the fluid jets exiting the adjacent longitudinal channels.

The disparities of the mixing rate in the width of the passage 10 are thus reduced, or even eliminated, after a shorter propagation distance of the mixture downstream of the mixing device 3. The thermal exchanges between the diphasic mixture and the second fluid F2, and thus the operation of the exchanger, are improved.

In addition, widening the downstream portion in the lateral direction y offers the possibility, in cases whereby the mass flow rate of the diphasic mixture in the longitudinal channel 32 is relatively high, of causing the flow of the mixture to slow down at the downstream portion, and thus of reducing the pressure losses experienced by the diphasic mixture at the outlet of the longitudinal channel 32, when it irrigates the exchange corrugations located downstream of the mixing device 3.

Preferably, several channels of the series of longitudinal channels 32, preferably all, are configured according to the invention and can comprise all or some of the features described hereafter.

Preferably, the downstream portion 324 emerges at a downstream face 326 of the mixing device 3, with the second outlet 322 being provided at the downstream face 326. At least part of the first phase 61 flowing into the lateral channel 31 supplies the opening 34 in order to flow into the longitudinal channel where the mixing occurs. The second phase 62 successively flows into the upstream 323 and downstream 324 portions. The mixture is distributed via the second outlet 322.

Preferably, the downstream portion 324 has an increasing width D_(y) over the length L₄ toward the second outlet 322, preferably increasing over the entire length L₄.

It should be noted that widening the downstream portion in the longitudinal direction z can be induced on an ad hoc basis, one or more times, or even gradually, i.e. be continuously increasing, along all or part of the downstream portion 324.

Preferably, the width D of the downstream portion 324 continuously increases, i.e, gradually, over the entire length L₄ toward the second outlet 322. Thus, the disruptions that could cause sudden variations in channel width in the flow of the mixture are limited.

Preferably, the downstream portion 324 has a minimum width D_(m) and a maximum width D_(m), with the ratio D_(M)/D_(m) being greater than or equal to 1.1, preferably greater than or equal to 1.8 and/or less than or equal to 4. Such a dimensional ratio allows the width of the longitudinal channel 32 to be sufficiently increased at the end 322, yet without excessively increasing the length of the longitudinal channel 32 in the direction z and maintaining the simplicity of machining the longitudinal channel 32.

In particular, the width D_(m) can range between 6 and 25 mm, preferably between 8 and 20 mm.

It also should be noted that a mixing device according to the invention can be intended to be arranged in a passage 10 that is provided, downstream of the mixing device, with at least one exchange corrugation comprising exchange channels each having a width ranging between 0.6 and 2 mm, preferably a width of at least 0.7 mm and/or at most 1.5 mm.

Preferably, the minimum width D_(m) is measured at the end 324 a of the downstream portion 324 and the maximum width D_(m) is measured at the second outlet 322.

Advantageously, the longitudinal channel 32 is defined by lateral walls 325 forming, in a longitudinal section plane that is parallel to the longitudinal direction z and to the lateral direction y, an external profile of said channel 32 with an axis of symmetry AA′ parallel to the longitudinal direction z.

It should be noted that the lateral walls 325 of the channel are preferably erected in a direction that is orthogonal to the longitudinal z and lateral y directions. The walls 325 advantageously have a height, measured in the direction x, that is constant over the entire length of the channel 32.

Alternatively, a variation in the height of the walls 325 can be contemplated, in particular an increase in said height toward the second outlet 322, i.e. a downstream portion 324, the depth of which increases toward the second outlet 322, until it optionally reaches the height of the passage 10 at the second outlet 322, This provides an additional degree of freedom for increasing the fluid passage section of the downstream portion 324 and thus slow down the fluid so that it also can be homogenized in the height of the passage 10.

Advantageously, at least part of the downstream portion 324 has a curvilinear external profile, preferably a convex external profile. FIG. 4 schematically shows an embodiment of a longitudinal channel 32 comprising such a downstream portion 324. The presence of a curvilinear external profile at the downstream portion provides better guidance for the flow of the fluid in the downstream portion to its outlet from the mixing device, in particular avoiding any separation phenomena, fluid recirculation or turbulence that could result from sharp edges on the walls and would cause undesirable additional pressure losses on the fluid.

It is also possible that all or part of the downstream portion 324 has, as a longitudinal section in a plane parallel to the longitudinal direction z and to the lateral direction y, an external profile in the form of an isosceles trapezoid, with the lateral walls at this portion being straight walls. FIG. 5 schematically shows an example in which the entire downstream portion 324 has such an external profile.

In particular, by considering a downstream face 326 of the mixing device 3 at which the downstream portion 324 emerges, the external profile can form an angle θ, measured between the tangent T to said external profile at the point of intersection with the downstream face 326 and the axis of symmetry AA′, that ranges between 5 and 85°. These values allow the width of the channel 32 at the second outlet 322 to be sufficiently increased in order to promote better distribution of the diphasic fluid F1 in the width of the exchanger in the direction y, yet without creating an excessively fast widening that could cause pressure losses in the fluid F1 and without excessively increasing the length L₄ and therefore the length of the mixing device 3.

FIG. 9 shows an embodiment in which the widening of the downstream portion in the longitudinal direction z is induced in an ad hoc manner, at once, at the end 324 a.

Preferably, the upstream portion 323 is connected to the downstream portion 324 by its end 324 a.

Advantageously, the upstream portion 323 has a length L₃, measured in the longitudinal direction z with the ratio L₃/L₄, that ranges between 1 and 15, preferably between 3 and 12.

By way of an example, the length L₄ can range between 5 and 40 mm. The length L₃ can range between 30 and 70 mm.

Advantageously, said at least one opening 34 emerges into the longitudinal channel 32 at its upstream portion 323, preferably at a distance L_(z) from the end 324 a of the downstream portion 324, with L_(z) at least being equal to 4%, more preferably ranging between 7 and 90%, and even more preferably ranging from 10 to 50%, of the length L₃ of the upstream portion 323. In particular, the opening 34 can emerge at a distance L_(z) ranging between 3 and 70 mm from the end 324 a of the downstream portion 324. Advantageously, the one or more opening(s) 34 of a longitudinal channel 32 all emerge at its downstream portion 323. The mixing device advantageously is devoid of an opening 34 emerging at its upstream portion 324, Thus, the first phase 61 and the second phase 62 are mixed far enough upstream of the downstream portion 324 so that, on the one hand, the diphasic fluid has the time to properly homogenize before entering the downstream portion 324 and, on the other hand, so that any recirculation zones for the fluid in the downstream portion 324 do not disrupt the flow of the first phase 61 via the opening 34 of the lateral channel 31 to the longitudinal channel 32, which could induce poor distribution. The higher speed of the second phase 62 in the portion 323 of the channel 32 compared to the speed of the fluid F1 in the portion 324 also allows the passage of the phase 61 from the channel 31 to the channel 32 via the opening 34 to be facilitated due to the high inertia of the phase 61 by the phase 62 and the resulting drive.

Preferably, it should be noted that the position of the at least one opening 34 in the longitudinal direction z varies between the longitudinal channels. It is particularly for this reason that some openings 34 can be closer to the end 324 a than others.

Furthermore, it should be noted that, within the scope of the invention, the longitudinal channels advantageously have identical dimensional features, i.e. the same external profile, the same depth, the same ratio L₃/L₄, the same distance L_(z), although it is possible in some configurations to vary at least one feature of at least one channel relative to the others, in particular the ratio of the lengths of the downstream and upstream portions.

Preferably, and as shown in FIG. 4 in particular, all or some of the upstream portion 323 has a straight external profile with a constant width D₃, preferably equal to the minimum width D_(m) of the downstream portion 324. According to one possibility, it is possible to contemplate that the upstream portion 323 has a variable width D₃ over all or some of its length, with D_(y) being greater than the maximum value that can be reached by D₃.

FIG. 6 and FIG. 7 schematically show embodiments in which the longitudinal channel 32 comprises at least one obstacle 327 arranged so as to sub-divide the downstream portion 324 into a plurality of intermediate channels 328 emerging at the second outlet 322.

This prevents the mixture from completely flowing in the longitudinal direction z and forces the flow to widen in the lateral direction y. The creation of intermediate channels is particularly advantageous when the mass flow rate in the longitudinal channel 32 is relatively high, since in this case the mixture has significant inertia in the longitudinal direction z, i.e, it tends to continue to flow in the direction z, even when the longitudinal channel widens.

Installing one or more obstacle(s) allows the direction of flow of the diphasic mixture to be modified by providing a component in the direction y at its speed. The angular opening of the fluid jet at the outlet of the longitudinal channel is thus increased, thereby providing a larger number of exchange channels positioned downstream of the mixing device.

Obstacles also can be used to keep the fluid passage section at the downstream portion constant or quasi-constant, or optionally to reduce said section, despite the widening thereof. It should be noted that “fluid passage section” is understood to be the surface through which the fluid flows measured perpendicular to the longitudinal direction z; this is to ensure lateral expansion of the mixture, yet without increasing the fluid passage section.

The pressure losses are thus rebalanced along the longitudinal channel.

Preferably, at the second outlet 322, the total surface of said obstacle 327, measured in a transverse section plane perpendicular to the longitudinal direction z, is between 20 and 80%, preferably between 30 and 70%, of the total fluid passage section of the downstream portion 324 measured in said transverse section plane.

In the case of several obstacles, the total surface is understood to be the sum of the surfaces of each obstacle.

In particular, provision can be made for the surface of the obstacle, measured at a distance of 1 mm in the longitudinal direction z, in the direction of the flow of the fluid, after the point of appearance in the channel 32, i.e. at a position, called impact position, located 1 mm after the point of appearance of the obstacle where the fluid impacts the obstacle, to represent between 1% and 80% of the fluid passage section of the channel 32 determined in a transverse section plane positioned at the impact position.

In a particular embodiment, the longitudinal channel 32 further comprises at least one balancing channel 329 fluidly connecting the intermediate channels 328. This allows the fluid pressures between the intermediate channels 328 to be rebalanced, in the event that there are disparities in the fluid flow and pressure rate between the intermediate channels. FIG. 8 shows an example of such a configuration.

Advantageously, an even number of intermediate channels is provided in order to maintain distribution symmetry along the axis AA′ of the mixture within the longitudinal channel.

The one or more obstacle(s) can be manufactured with the longitudinal channel by milling, by injection molding a metal, by electro-erosion or by laser machining. An additive manufacturing method also can be contemplated.

Preferably, the height of the obstacles 327 is equal to those of the lateral walls of the longitudinal channel.

Preferably, said at least one obstacle 327 has a width dy, measured in the lateral direction y, that increases toward the second outlet 322, preferably with a curvilinear, convex and/or concave external profile. This allows the obstacle to be shaped so as to avoid additional pressure losses of the fluid F1 in the downstream portion 324 of the channel 32 by detaching the fluid at the walls of the obstacle or due to zones for recirculating the fluid.

Preferably, several passages 10 of the first set, advantageously all the passages 10, comprise a mixing device according to the invention.

Preferably, at least one passage 20 of the second set is arranged between at least one consecutive pair of passages 10 of the first set.

Preferably, the longitudinal channels 32 of the mixing device 3 are separated from each other by a constant distance D_(A) measured parallel to the longitudinal direction y.

It should be noted that the positions y_(i), y_(i+1), y_(i+2) . . . of each channel in the lateral direction y can be determined by considering the position of the center of each channel in the lateral direction y. For example, by considering channels in the form of parallelepiped grooves, such as those shown in FIG. 2 , the position of a channel in the direction y corresponds to the position of the axis of symmetry of the channel located at an equal distance from the lateral walls of the channel, as shown in FIG. 2 .

The distance D_(A) can range between 10 and 40 mm, and preferably can be greater than or equal to 20 mm and less than or equal to 30 mm.

In order to illustrate the homogenization effect that is obtained with the invention, FIG. 11 shows the results of a simulation of the propagation of a two-phase mixture in a longitudinal channel of a conventional mixing device (configuration A) and in a longitudinal channel of a mixing device according to one embodiment of the invention (configuration B).

In configuration A, the mixing device was in the form of a grooved bar comprising, as longitudinal channels, a series of parallelepiped grooves succeeding each other at regular intervals of 30 mm, Each groove is 7 mm wide, 70 mm long and 7 mm high.

In configuration B, which is partially schematically shown in FIG. 10 , the mixing devices were in the form of grooved bars with grooves succeeding each other at regular intervals of 30 mm. Each groove was in the form of a longitudinal channel with an upstream portion 323 that is 7 mm wide, 63 mm long and 7 mm high. The downstream portion 324 had a frustoconical shape that was 7 mm wide at the end 324 a and 14 mm wide at the second outlet 322. The upstream portion 323 was 7 mm long and 7 mm high. An isosceles triangle obstacle was placed in the downstream portion 324, symmetrically relative to the axis of symmetry AA′, being 7 mm high in the direction z and having a base width of 7 mm at the second outlet 322. The width D_(M) was twice as high as D₃. The ratio L₃/L₄ was 8 and the length L_(z) was 5 mm. The angle θ was 45°. It should be noted that configuration B corresponds to the particular case whereby the fluid passage section of the downstream portion is kept constant in the longitudinal direction z due to the presence of the obstacle, although the width of said portion increases toward the second outlet 322.

The longitudinal channels of the mixing devices of configurations A and B were arranged according to the same number and at identical positions y_(i), y_(i+1), . . . in the lateral direction y.

In configurations A and B, “serrated” type corrugations 11, i.e. partially offset, were arranged at the outlet of the mixing devices in each passage. These corrugations were of the “⅛” serrated” type (1″=1 inch=25.4 mm), i.e. with a serration length of 25.4/8=3.18 mm and had corrugations with a density of 23 fins per inch (1 inch=25.4 millimeters), measured in the lateral direction y.

The simulation is a three-dimensional CFD (Computational Fluid Dynamics) type computation using the finite elements method.

FIG. 11 shows the evolution of the value of the smallest dimensionless speed of the fluid in the longitudinal direction z (denoted Vz) measured on successive sections of the corrugations located after the outlet 322 in planes parallel to the directions x and y, for several values of distances between the outlet 322 and said planes. These speed values represent the quality of the fluid distribution in the corrugations: a negative value indicates the presence of a recirculation zone, with fluid stagnant at the center of the zone. A zero value indicates the presence of stagnant fluid. As the stagnant fluid is not renewed, it does not participate in the heat exchange and reduces the overall efficiency of the exchanger.

A fluid distribution performance indicator is the minimum necessary distance in the longitudinal direction z from which all the fluid has a positive speed in the longitudinal direction z.

It can be seen that the minimum necessary distance is reduced from 45 to 31 mm, that is a reduction of 35% in configuration B according to the invention relative to the conventional configuration A. By virtue of the invention, the homogenization of the two-phase mixture distributed by a mixing device is significantly improved and the efficiency of the exchanger is improved.

FIG. 12 and FIG. 13 show examples of methods implementing one or more exchanger(s) according to the invention.

FIG. 12 schematically shows a method for liquefying a hydrocarbon stream 102 as a second fluid F2, which can be natural gas, optionally pre-treated, for example, having undergone the separation of at least one of the following constituent elements: water, carbon dioxide, sulfur compounds, methanol, mercury, before being introduced into the heat exchanger 1.

Preferably, the hydrocarbon stream comprises, as a mole fraction, at least 60% methane, preferably at least 80%.

The hydrocarbon stream 102 and the cooling stream 202 enter the exchanger 1, respectively via a third inlet 25 and a fourth inlet 21, in order to circulate therein in dedicated passages of the exchanger in directions parallel to the longitudinal direction z, which is substantially vertical during operation. The hydrocarbon stream 102 circulates through the passages 20 of the second set supplied by the third inlet 25. The cooling stream 202 circulates through a third set of passages arranged within the stack forming the exchanger 1. These streams exit via a third outlet 22 and a first outlet 23. The passages of the second and third sets are arranged, in whole or in part, alternately and/or adjacent to all or some of the passages 10 of the first set.

Advantageously, the fourth inlet 21 for the cooling stream 202 and the third inlet 25 for the hydrocarbon stream 102 are arranged such that the cooling stream 202, and optionally the hydrocarbon stream 102, flows co-currently downwardly, toward a second end 1 b of the exchanger, which is located at a level lower than that of a first end 1 a of said exchanger. Preferably, the first end 1 a corresponds to the hot end of the exchanger 1, i.e. the entry point of the exchanger where a fluid is introduced at the highest temperature of the temperatures of the exchanger, this entry point can be the fourth inlet 21 or the third inlet 25, depending on the relevant method.

The hydrocarbon stream 102 can be introduced into the exchanger 1 at a temperature ranging between −130 and 40° C.

According to one possibility, the hydrocarbon stream 102 is introduced into the exchanger 1 in the fully gaseous or partially liquefied state at a temperature ranging between −80 and −35° C.

According to another possibility, the hydrocarbon stream 102 is introduced into the exchanger 1 in a fully liquefied state at a temperature ranging between −130 and −100° C.

The cooling stream 201 exiting the exchanger 1 is expanded by an expansion component T3, such as a turbine, a valve or a combination of a turbine and a valve, so as to form a diphasic cooling stream 203 comprising a first phase and a second phase. The diphasic cooling stream 203 forms the previously considered first fluid F1. At least part of the diphasic cooling stream 203 originating from the expansion is introduced into a separator component 27. The separator component can be any device adapted to separate a diphasic fluid into a predominantly gaseous stream, on the one hand, and a predominantly liquid stream, on the other hand.

The second phase 62 is introduced via the manifold 52, which supplies the second inlets 321 of mixing devices 3 arranged in the passages 10 of the first set. The first phase 61 is introduced via the first manifold 30, which supplies the first inlets 311 of mixing devices 3 arranged in each passage 10 (not shown in FIG. 9 ).

Preferably, the second phase is introduced via an inlet located in the region of the second end 1 b corresponding to the cold end of the exchanger 1, i.e. the inlet point in the exchanger where a fluid is introduced at the lowest temperature of the temperatures of the fluids in the exchanger.

The two phases 61, 62 of the diphasic stream 203 are recombined within the exchanger 1 and distributed in the liquid-gas mixture state in the passages 10 of the exchanger 1 each provided with mixing devices 3 according to the invention.

Preferably, the diphasic cooling stream 203 is introduced into the heat exchanger 1 at a first temperature T1 ranging between −120 and −160° C. and exits the heat exchanger 1 at a second temperature T2 higher than the first temperature T1, preferably with T2 ranging between −35 and −130° C.

According to another possibility, the diphasic cooling stream 203 is introduced into the heat exchanger 1 at a first temperature T1 ranging between −130 and −80° C. and exits the heat exchanger 1 at a second temperature T2 higher than the first temperature T1, preferably with T2 ranging between −10 and 50° C.

Said at least part of the diphasic cooling stream 203 upwardly flows through the passages 10 and is vaporized by counter-currently cooling the natural gas 102 and the cooling stream 202. A cooled and/or at least partially liquefied hydrocarbon stream 101 is thus obtained at the outlet of the exchanger 1.

The vaporized cooling stream exits the exchanger 1 via a second outlet 42 connected to the manifold 55 in order to be compressed by a compressor and then cooled in an indirect heat exchanger by exchanging heat with an external cooling fluid, for example, water or air (at 26 in FIG. 12 ). The pressure of the cooling stream at the outlet of the compressor can range between 2 MPa and 9 MPa. The temperature of the cooling stream at the outlet of the indirect heat exchanger can range between 10° C. and 45° C.

In the method described in FIG. 12 , the cooling stream is not split into separate fractions, but, in order to optimize the approach in the exchanger 1, the cooling stream can also be separated into two or three fractions, with each fraction being expanded at a different pressure level, and then sent to various stages of the compressor.

Preferably, the cooling stream 202 contains hydrocarbons having at most 5 carbon atoms, preferably at most three, more preferably at most two.

Preferably, the cooling stream 202 is formed, for example, by a mixture of hydrocarbons and nitrogen, such as a mixture of methane, ethane and nitrogen, but can also contain propane, butane, isobutane, n-butane, pentane, isopentane, n-pentane and/or ethylene.

The mole fraction proportions (%) of the components of the cooling stream can be:

-   -   Nitrogen; 0% to 10%;     -   Methane: 20% to 70%,     -   Ethane: 30% to 70%;     -   Ethylene: 20 to 70%     -   Propane: 0% to 20%     -   n-butane: 0% to 30%;     -   Isopentane: 0% to 20%.

Optionally, the cooling stream can comprise, as a replacement for ethane, ethylene and, as a replacement for all or some of the propane, compounds of the C4, C5 type.

Preferably, the natural gas exits the exchanger 1 at least partially liquefied 101 at a temperature that is preferably higher than at least 10° C. in relation to the bubble temperature of the liquefied natural gas produced at atmospheric pressure (the bubble temperature denotes the temperature at which the first vapor bubbles form in a liquid natural gas at a given pressure) and at a pressure that is identical to the inlet pressure of the natural gas, to the nearest pressure losses. For example, the natural gas exits the exchanger 1 at a temperature ranging between −100° C. and −162° C. and at a pressure ranging between 2 MPa and 7 MPa. Under these temperature and pressure conditions, and depending on its composition, the natural gas does not generally remain liquid after expansion to atmospheric pressure.

Advantageously, the method for liquefying a hydrocarbon stream according to the invention can implement one or more additional refrigeration cycle(s) performed upstream of the main refrigeration cycle described above, so as to pre-cool the hydrocarbon stream.

FIG. 13 schematically shows a method for liquefying a hydrocarbon stream such as natural gas comprising an additional refrigeration cycle, in which the natural gas is cooled to a temperature close to its dew point using at least two different expansion levels in order to increase the efficiency of the cycle. This additional refrigeration cycle is implemented by means of an additional cooling stream 300 in an additional heat exchanger 2, called pre-cooling exchanger, arranged upstream of the heat exchanger 1 in the direction of the flow of the hydrocarbon stream 110, which then forms the liquefaction exchanger.

In this embodiment, a supply stream 110 arrives, for example, at a pressure ranging between 2.5 MPa and 7 MPa and at a temperature ranging between 20° C. and 60° C. With the supply stream 110 comprising a mixture of hydrocarbons such as natural gas, the cooling stream 202 and an additional cooling stream 300 enter the additional exchanger 2 in order to circulate therein in parallel and co-current directions in the downward direction.

A cooled, or even at least partially liquefied, hydrocarbon stream 102, exits the pre-cooling exchanger 2. Preferably, the hydrocarbon stream 102 exits in the gaseous or partially liquefied state, for example, at a temperature ranging between −35° C. and −70° C. The cooling stream 202 can also exit the exchanger 2 completely condensed, for example, at a temperature ranging between −35° C. and −70° C., The stream 102 is then introduced into the exchanger 1.

As can be seen in FIG. 13 , the stream 203 is vaporized in the exchanger 1 and exits the exchanger in order to be compressed by the compressor K2 and then cooled in the indirect heat exchanger C2 by exchanging heat with an external cooling fluid, for example, water or air. The cooling stream originating from the exchanger C2 is then returned to the additional exchanger 2.

The additional cooling stream 300 can be formed by a mixture of hydrocarbons such as a mixture of ethane and propane, but can also contain methane, ethylene, propylene, butane and/or pentane. The mole fraction proportions (%) of the components of the first coolant mixture can be:

-   -   Ethane: 30% to 70%;     -   Propane: 30% to 70%;     -   Butane: 0% to 20%;

In the additional exchanger 2, which is also of the brazed plate and fin type, at least two partial streams originating from the additional cooling stream 300 are drawn from the exchanger on at least two distinct outlet points and are then expanded at different pressure levels, giving rise to partial diphasic expanded streams each comprising a first phase and a second phase. At least part of these partial diphasic streams is introduced into respective separator components 24, 25, 26.

In the embodiment of FIG. 13 , three fractions, also called partial flow rates or streams, 301, 302, 303 of the additional cooling stream 300 in the first phase are successively withdrawn.

The gaseous and liquid phases separated by each separator component are introduced via separate inlets of the additional heat exchanger 2 and are recombined within mixing devices (not shown), so as to form at least two coolant fluids introduced into dedicated coolant passages in the liquid-gas mixture state. Alternatively, only the first phase is injected into the exchanger 2 and the gas phase is directed toward the inlet of the compression stages of the compressor K1. These coolants are vaporized in the additional exchanger 2 by exchanging heat with the supply stream 110 and the cooling stream 202 and the additional cooling stream 300.

Advantageously, at least two types of mixing devices 2 are arranged in the additional exchanger, such as those that can be arranged within the exchanger 1 according to the invention. Thus, the additional exchanger comprises at least two coolant passages each comprising a mixing device, with these devices comprising one or more of the features previously described for the first and second mixing devices 3A, 3B.

The vaporized coolants in their respective coolant passages are sent to various stages of the compressor K1, compressed and then condensed in a condenser by exchanging heat with an external cooling fluid, for example, water or air. The stream originating from the condenser is returned to the additional exchanger 2. The pressure of the first cooling stream at the outlet of the compressor K1 can range between 2 MPa and 6 MPa. The temperature of the additional cooling stream at the outlet of the condenser C1 can range between 10° C. and 45° C.

Preferably, the coolants upwardly flow from one end 2 b of the additional exchanger 2 to another end 2 a in the longitudinal direction z. The end 2 b corresponds to the cold end of the additional exchanger 2 where the coolant is introduced at the lowest temperature of the temperatures of the additional exchanger 2.

Of course, the invention is not limited to the particular examples described and illustrated in the present application. Other alternative embodiments or embodiments within the scope of a person skilled in the art also can be contemplated without departing from the scope of the invention. For example, other configurations for injecting and extracting fluids into/from the exchanger, other flow courses and directions for the fluids, other types of fluids, other forms of mixing devices, of lateral and longitudinal channels, etc. obviously can be contemplated, depending on the constraints imposed by the method to be implemented.

It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above. 

1.-15. (canceled)
 16. A mixing device for distributing a mixture of a first phase and a second phase of a first fluid in a longitudinal direction in at least one passage of a heat exchanger, said mixing device comprising: at least one lateral channel configured for the first phase to flow from at least one first inlet; a series of longitudinal channels extending in the longitudinal direction and each configured for the second phase to flow from a second inlet to a second outlet, said longitudinal channels succeeding each other in a lateral direction orthogonal to the longitudinal direction; and at least one opening fluidly connecting said lateral channel to at least one longitudinal channel such that the mixing device is configured to distribute a mixture of the first phase and the second phase via the second outlet of said longitudinal channel, wherein said at least one longitudinal channel of the mixing device is divided, in the longitudinal direction, into an upstream portion having a length L₃ measured in the longitudinal direction ad a width D₃ measured in the lateral direction, and a downstream portion having a length L₄ measured in the longitudinal direction and a width D₄ measured in the lateral direction, with the downstream portion being arranged between the upstream portion and the second outlet, said downstream portion having, at any point of its length, a width that is greater than the width of the upstream portion.
 17. The device as claimed in claim 16, wherein the downstream portion has a continuous increasing width over the entire length toward the second outlet.
 18. The device as claimed in claim 16, wherein all or part of the downstream portion has, as a longitudinal section in a plane parallel to the longitudinal direction and to the lateral direction, an external profile in the form of an isosceles trapezoid.
 19. The device as claimed in claim 16, wherein the downstream portion emerges at a downstream face of the mixing device, the external profile forming an angle θ, measured between the tangent to said external profile at the point of intersection with the downstream face and the axis of symmetry of the longitudinal channel, ranging between 5 and 85°.
 20. The device as claimed in claim 16, wherein the upstream portion of the longitudinal channel is connected to the downstream portion by one end, said at least one opening emerging into said longitudinal channel at the upstream portion at a distance L_(z) from the end, wherein distance L_(z) is greater than or equal to 4% of the length L₃ of the upstream portion.
 21. The device as claimed in claim 16, wherein the at least one opening is arranged such that, when the first phase flows from the first inlet of the lateral channel and the second phase flows from the second inlet of the longitudinal channel, the mixing of the first phase and the second phase occurs upstream of the downstream portion.
 22. The device as claimed in claim 16, wherein the one or more opening(s) of the mixing device all emerge at the upstream portion of a longitudinal channel.
 23. The device as claimed in claim 16, wherein each longitudinal channel of the series of longitudinal channels comprises at least one opening emerging at the upstream portion, with the position of the at least one opening in the longitudinal direction varying between the longitudinal channels.
 24. The device as claimed in claim 16, wherein the length L₃ of the upstream portion and the length L₄ of the downstream portion are such that the ratio L₃/L₄ ranges between 1 and
 15. 25. The device as claimed in claim 16, wherein the downstream portion has a depth, measured in a direction, called stacking direction, that is perpendicular to the longitudinal direction and perpendicular to the lateral direction, increasing toward the second outlet.
 26. The device as claimed in claim 16, wherein the longitudinal channel comprises at least one obstacle arranged so as to sub-divide the downstream portion into a plurality of intermediate channels emerging at the second outlet wherein said intermediate channels are arranged symmetrically with respect to the axis of symmetry of the longitudinal channel.
 27. A heat exchange facility comprising: a heat exchanger comprising a plurality of plates arranged parallel to each other and to a longitudinal direction, said plates being stacked in a spaced-apart manner so as to together define at least a first set of passages configured for a first fluid to flow in the longitudinal direction and at least one second set of passages configured for the flow of a second fluid to be brought into a heat exchange relationship with the first fluid; a source of a first phase of the first fluid fluidly connected to at least one first manifold of the heat exchanger; a source of a second phase of the first fluid fluidly connected to at least one second manifold of the heat exchanger; a mixing device as defined by claim 16, said mixing device being arranged in at least one passage of the first series and being configured to distribute the first fluid formed by a mixture of the first phase) and the second phase in said passage of the first series, the first inlet of the lateral channel being in fluid communication with said first manifold, and the second inlet being in fluid communication with the second manifold, the first phase being a liquid phase and the second phase being a gaseous phase.
 28. A method for mixing a first phase and a second phase of a first fluid in a mixing device as defined by claim 16, said method comprising the following steps: i) introducing the first phase of the first fluid via at least one first inlet of the lateral channel; ii) introducing the second phase of the first fluid via a second inlet of each longitudinal channel, the second phase flowing in each longitudinal channel in the longitudinal direction to a second outlet of said longitudinal channel; iii) flowing at least part of the first phase from the lateral channel toward the longitudinal channel via the opening so as to mix the first phase with the second phase in the longitudinal channel; iv) distributing the mixture of the first phase and the second phase via the second outlet of each longitudinal channel.
 29. The mixing method as claimed in claim 28, wherein the first phase is mixed with the second phase upstream of the downstream portion.
 30. A method for liquefying a hydrocarbon stream as the second fluid by exchanging heat with at least one diphasic cooling stream as the first fluid, said method implementing a mixing method as claimed in claim 28 and comprising the following steps: a) introducing the hydrocarbon stream into a second set of passages of a heat exchanger; b) introducing a cooling stream into a third set of passages of the heat exchanger; c) discharging the cooling stream from the heat exchanger and expanding the cooling stream to at least one pressure level so as to produce at least one diphasic cooling stream; d) separating at least part of the diphasic cooling stream originating from step c) into a second phase and a first phase; e) arranging a mixing device in at least one passage of a first set of passages of the heat exchanger; f) introducing at least part of the second phase and at least part of the first phase into the mixing device so as to obtain a first fluid formed by a mixture of the first phase and the second phase at the outlet of the mixing device; g) vaporizing at least part of the first fluid originating from step f) in the passage by exchanging heat with at least the hydrocarbon stream so as to obtain a cooled and/or at least partially liquefied hydrocarbon stream at the outlet of the exchanger. 